Just to add, this is one I have, uses the same tank as your grill. Unit is self contained, tank is in the back.
Unvented propane heater will add a ton of moisture into your house.
Meant to comment on this over the weekend. Walrus is correct that unvented propane heater will put a lot of moisture into the house. Now the question is, is that a bad thing especially when you factor in the amount of use and what your primary heating source is.
I have oil fired forced air heating and run a humidifier tied into the furnace to up the humidity as forced air is very dry. Also, how much will the heater be used. In Muddy's case and Pep's example, I don't think either heater will be used long enough to be a problem with moisture and it may be a benefit if their air is dry.
I believe that knowing that moisture could be an issue and to be aware of it and paying attention while using unvented propane and only using it as supplemental heat, problems would be minimal.
Now to my concern,,,,,,,,,,,,,,,,,,,,,,,,,,,,not crazy about having a propane bottle inside my house. But now that I think of it, I have several propane tanks in my attached garage